sideways mortice and tenons

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26 Aug 2019
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|Hey all
I am making some windows for a client and the measurements they gave me are a bit vague, resulting in the vertical and horizontal sections needing to be rotated through 90' in order to be correct. to clarify the front of the frame is now the side and the side the front. the front was 40mm and is now 50mm and vice versa. I was fortunate to have machined the parts long so was able to still achieve the correct outside dimensions. However the tenons were cut on the end of the horizontals (are they the rails?) and in rotating them through 90' the tenons now run through the sides side to side rather than lengthways.
I am sorry if this is hard to picture - I am unable to post a pic at the moment. I hope my ramblings make sense!

The question is does it affect the integrity of the whole part if the tenons are altered this way? Can i get away with it? It will, obviously, be enclosed and so not visible when assembled, but I would not wish to compromise the strength if it is a major factor. The tenons are large enough to be strong.

I am embarrassed to ask this question so early in my UKW career, but needs must.

Thanks in advance

I just finished a book by Marc Spagnuolu, it's called "Essential Joinery" but it's only about joints. There are many ways to do the same thing (or so it seems). One point he made is that the mortice and tenon get their strength from the fit of the joint and the glue between the sides of the joint (which are on side grain). Where you have rotated the tenon (and then cut mortices to match) you now have the long glue joint (line) that's now against end grain e.g. it won't be a long strong joint. He makes the point that you don't have to get a good fit on the edges of the tenon because it doesn't add to the strength and he says you can make square tenons or round them off or leave a gap because the strength is on the other sides (see the problem). If you had cut mortices and then filled them in and had another go that wouldn't have been so bad. Or if you had cut mortices that are now visible and so had to be replaced.

There's a financial cost to leaving things as they are. If there's a problem and you have to remove and replace then everything is scrapped and you wasted lots of time, whereas if you replaced the sections then the impact is reduced. If you confessed to your "crime" then a discount would have to be offered. If you keep quiet, how can you sleep at night? Clearly there is a problem with your client's changing requirements but it's for you to check that you have a common understanding.

Some mistakes can be covered up but the sensible thing would be to redo it? When Vauxhall (like Alfa and everyone else) produced cars that rusted away far too quickly, it took twenty years for buyers to accept that they had overcome their problems. Of course, if you had made 20 windows then you might be tempted to "fix it" e.g. pin the joint with hardwood dowels from behind etc. or console yourself that the strength isn't required because it's contained by the buildings structure - just how much movement do you expect? +1 for replace it.
I have simple rule. "Never bodge".

If you bodge and charge for it, expect twice the cost down the line.

This is a client bodge. Nuff said.
None of that is what you want to hear, is it? It doesn't stop it from being true, unfortunately.
I don't think that I am the only one who has travelled the bodge route only to find out later that it was a bad decision.
I try not to repeat that mistake on anything that actually matters...
Definitely not, as everyone else has said it's just going to be mostly end-grain to long-grain connection and even with the best glues I can guarantee you than in a couple of seasons the joints will pop and they will let moisture in and they will just either rot or fall apart with time (Quite quickly too!). Replace the pieces.

You owe it to your customer to provide work that is to the best of your ability, not some cowboy bodge job. It takes many years to garner a good reputation, that can all be lost on the back of a single bad job. If you haven't got a clue about how wood actually works firstly why are you making stuff that requires a great deal of knowledge about how wood works?
Learn from it and move on.

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